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Abstract

In this paper, we propose a high-speed 3D shape measurement technique based on the optimized composite fringe patterns and stereo-assisted structured light system. Stereo phase unwrapping, as a new-fashioned method for absolute phase retrieval based on the multi-view geometric constraints, can eliminate the phase ambiguities and obtain a continuous phase map without projecting any additional patterns. However, in order to ensure the stability of phase unwrapping, the period of fringe is generally around 20, which limits the accuracy of 3D measurement. To solve this problem, we develop an optimized method for designing the composite pattern, in which the speckle pattern is embedded into the conventional 4-step phase-shifting fringe patterns without compromising the fringe modulation, and thus the phase measurement accuracy. We also present a simple and effective evaluation criterion for the correlation quality of the designed speckle pattern in order to improve the matching accuracy significantly. When the embedded speckle pattern is demodulated, the periodic ambiguities in the wrapped phase can be eliminated by combining the adaptive window image correlation with geometry constraint. Finally, some mismatched regions are further corrected based on the proposed regional diffusion compensation technique (RDC). These proposed techniques constitute a complete computational framework that allows to effectively recover an accurate, unambiguous, and distortion-free 3D point cloud with only 4 projected patterns. Experimental results verify that our method can achieve high-speed, high-accuracy, robust 3D shape measurement with dense (64-period) fringe patterns at 5000 frames per second.

Fig. 5 (a) A speckle pattern is designed using the proposed method. (b) The period order map based on (a) is obtained using the proposed test method. (c) The error rate for phase unwrapping on the designed speckle patterns with different speckle size.

Fig. 7 The operation process of confirming period order based on geometry constraint and the adaptive window image correlation. (a) The wrapped phase obtained from main camera. (b) The speckle pattern obtained from main camera. (c) The wrapped phase obtained from auxiliary camera. (d) The speckle pattern obtained from auxiliary camera. (e) The correlation result obtained using the smaller L (5 pixels). (f) The period order map obtained using the smaller L (5 pixels). (g) The correlation result obtained using the larger L (10 pixels). (h) The period order map obtained using the larger L (10 pixels). (i) The enlarged detail of the region in (f). (j) The enlarged detail of the region in (h).

Fig. 9 (a) The elementary absolute phase map obtained from auxiliary camera. (b) The final absolute phase map obtained using the left-right consistency check. (c) The 3D reconstruction result obtained using (b). (d) The enlarged detail of the region in (c). (e) The elementary absolute phase map obtained from main camera. (f) The final absolute phase map obtained using RDC. (g) The 3D reconstruction result obtained using (f). (h) The enlarged detail of the region in (g).

Fig. 12 The phase measurement results of a standard ceramic plate. (a) The ceramic plate to be measured. (b) The 2D camera image (one of the four-step phase-shifting patterns) from main camera. (c) The wrapped phase is obtained using Eq. (12). (d) The demodulated speckle pattern is obtained using Eq. (15). (e) The phase order map based on geometry constraint. (f) The phase order map based on geometry constraint and the adaptive window image correlation. (g) The phase order map using left-right consistency check. (h) The phase order map using RDC. (i)-(l) The corresponding absolute phase map of (e)-(h).

Fig. 14 The measurement results of several objects. (a) A girl statue with a ceramic plate. (b) A Voltaire model and a statue of the Goddess with discontinuous surfaces. (c) The statue of Skadi. (d)-(f) The corresponding 3D reconstruction results of (a)-(c). (g)-(i) The corresponding enlarged detail of the region in (d)-(f).